A magneto-resistive head (hereinafter MR head) is used in a hard disk drive of a computer or a signal recording and reproducing apparatus, such as, for example, a video tape recorder. The MR head has good characteristics for reproducing a signal.
The MR head is a magnetic head using a magneto-resistive layer (hereinafter MR device). The MR device has characteristics in which the electric resistance thereof changes in accordance with a magnetic field adjacent to the MR device. Therefore, as the magnetic field adjacent to the MR device in the MR head changes in response to a signal recorded on a magnetic medium, the MR head provides a reproducing signal which is proportional to the resistance change of the MR device.
In the MR head, the reproducing signal is proportional only to the resistance change. In other words, the amplitude of the reproducing signal is proportional to the strength of the magnetic field adjacent to the MR head. As a result, the amplitude of the reproducing signal has no relation to the relative speed between the MR head and the magnetic medium. Further, the reproduction sensitivity of the MR head is greater than that of the ordinary magnetic head.
The MR head has nonlinear characteristics between the resistance change and the strength of magnetic field. To provide a reproducing signal proportional to the strength of the magnetic field from the MR head, it is necessary to provide a predetermined magnetic bias field to the MR device. For a device used to provide the magnetic bias field, it is preferable to dispose a shunt layer adjacent to the MR device, such as described in U.S. Pat. No. 5,010,433. The shunt layer is a electric current path disposed adjacent to the MR device. The electric current through the shunt layer provides the magnetic bias field.
In a prior arrangement shown in FIG. 15, an MR device 2 of 400 angstrom (.ANG.) thickness is formed on a glass substrate 1. A shunt layer 3 (a zirconium thin film 1500 angstrom (.ANG.) thick) is disposed on the MR device 2. Further, an aluminum electrode 4 and a protective SiO.sub.2 layer 5 are formed on the shunt layer 3.
Potential difference across the electrodes 4 causes an electric current to flow through the MR device 2 and the shunt layer 3. The current flowing through the shunt layer 3 produces a magnetic bias field to the MR device 2. Because of the magnetic bias field, the MR head provides a reproducing signal proportional to the strength of the magnetic field from a magnetic medium, such as, for example, a video tape.
Titanium (Ti), tantalum (Ta), molybdenum (Mo), gold (Au), niobium (Nb), zirconium (Zr), etc. have been used for the shunt layer in a conventional shunt bias MR head. A shunt layer of Ti, Au and Zr has a problem in that the material of the shunt layer and the MR device react with each other and result in the deterioration of the signal reproducing characteristics of the MR device. Mo is also unsuitable due to its extremely poor corrosion resistance.
A shunt layer having high electrical resistivity requires a thick shunt layer to provide a predetermined strength of magnetic bias field to the MR device. It is desirable for the shunt layer and the MR device to be narrow so that the MR head can reproduce high frequency signals.